This invention relates to a pressure-resistant helical corrugated pipe mainly adapted to be buried in the ground, so that telecommunication cables such as an electric cable and a telephone cable can be installed in such a corrugated pipe for the purpose of protecting such cables. Also, such a corrugated pipe is used as a water main pipe, a sewer pipe, or a liquid transport pipe used in a plant or a factory.
Among such conventional pressure-resistant helical corrugated pipes, the type of corrugated pipes adapted for underground use have been required to be pressure-resistant in order to withstand a great ground pressure. In a conventional underground pressure-resistant pipe (see, for example, Japanese Laid Open Utility Model Application No. 141889/86 field by the Applicant of the present application), a continuous reinforcing belt plate made of a thin metal plate is embedded in the pipe wall and extends over the top portion of the helical corrugation, the opposite side wall portions, extending from the top portion, and part of bottom portion.
However, when the metal reinforcing belt plate to be thus embedded in the pipe wall is of such a unitary construction that this plate can be disposed in the top portion and the opposite side wall portions, with its oppositely-projecting side edge portions disposed in part of the bottom portion as described above, the pipe is less flexible (though having a certain degree of flexibility) although its pressure-resistant strength to withstand the flattening is quite excellent. As a result, the pipe, when bent, inevitably has a large radius of curvature. Thus, it is difficult to provide a pipe which can be bent into a small radius of curvature. Further, the shaping and working of the metal reinforcing belt plate are difficult. Another problem is that it is difficult to obtain helical corrugated pipes having different helical pitches, using such a metal reinforcing belt plate of an identical shape.